For my first 2.5 years of cleaning I used old fashioned brushes and after completing all my WETT courses early 2017 and learning of new techniques in the industry I was a quick convert!! Loving this new technique! Its affects can best been seen here.
For harder jobs and an additional charge I can use a cable whip that doesn't damage and will completely clean the liner of any hard stuck residue. This method will always be done after a chimney fire to ensure there are no issues with the liner.